1. Field of the Invention
The present invention relates to an apparatus for securing boxes of merchandise to a pallet through the use of a continuous stretch wrap layer applied to the exterior of the loaded pallet. The invention also relates to gripping and cutting mechanisms utilized in conjunction with said mechanism intended to increase the speed of said operations. More specifically, the invention relates to a single station wrapping mechanism utilized in association with a conveyor system having a rotary arm wrapping mechanism which utilizes particularized gripping and termination mechanisms and a method for use thereof which allows for a more stable and efficient gripping of wrapping film in preparation to a wrapping cycle and more precise cutting of said film subsequent to said wrapping cycle and which is adapted to leave said film in a condition for more efficient gripping during the next wrapping cycle.
2. Description of the Prior Art
Modern transportation methods of goods involve the packaging of discreet manufactured units within cardboard enclosures. These cardboard enclosures are frequently stacked on a wooden pallet in standard lot sizes for easier transportation in large quantities. Pallets are adapted to be easily located and transported through the use of a forklift and furthermore may be transported along a conveyor. Because the palleted merchandise must be moved by mechanical means often involving stopping, starting and changing directions, the palleted load must be secured upon the pallet. The first method of securing the load is to stack the objects thereon in an interlocking pattern which maximizes the stability of the stacked load. The weight and location of the goods are evenly distributed on the pallet so that minimal shifting occurs during transportation. Furthermore, the pallet pattern, as such stacking practices are called, is designed to prevent collapse of materials in the lower portion of the stack.
An additional method for securing "palletized" materials to the pallet is to enclose the palletized stack in a plastic wrap or film. This is especially useful when all of the palletized materials are not of identical shape and size. A plastic stretch wrap is applied to the exterior of the pallet stack and continuously wrapped around the exterior of the stack to effectively form a solid cube of materials. Due to the weight and size of the now unitary structure mounted on the pallet, shifting is less likely to occur during transportation of the palletized merchandise. In order to apply the stretchable plastic wrap to the pallet, the wrap is prestretched to a specified limit, applied to the palletized stack of merchandise with certain force, and allowed to shrink back against the exterior of the palletized stack forming a tight enclosure around the stacked materials. The physical wrapping of the pallet stack usually involves the helical progression of wrap from top to bottom, or vice versa, in a repeated fashion, until the stack has been adequately secured. Care must be taken that the wrap is applied with the proper amount of prestretch and tension, commonly known as force to the load, otherwise the stack may become unstable or the contents may be crushed by the force of the stretched film.
A number of devices have been proposed in the prior art to perform this wrapping function. A representative sample of these devices are disclosed in Ball, et al., U.S. Pat. No. 4,772,170, issued Feb. 2, 1988; Salzsauler, U.S. Pat. No. 4,934,132, issued Jun. 19, 1990; and Haloila, U.S. Pat. No. 4,993,209, issued Feb. 19, 1991. Each of the references discloses a device which generally comprises a support stand having a rotating swing arm mounted thereon and a swing arm having a carriage at the end thereof which contains the plastic wrap. The Haloila reference utilizes a fixed circular track surrounding the pallet having a carriage mounted thereupon to achieve the same objective. The carriage containing the plastic wrap is continuously rotated in a circular fashion above the palletized stack which is helically encased in at least one layer of film while the carriage rotates thereabout while moving vertically along its support column.
Buettner, U.S. Pat. No. 3,930,442, issued Jan. 6, 1976, Schulman, U.S. Pat. No. 4,109,445, issued Aug. 29, 1978, and Haloila, U.S. Pat. No. 4,936,080, issued Jun. 26, 1990, all disclose similar wrapping devices as those previously described, however each of these three references further discloses the use of a conveyor to transport the palletized goods to the wrapping station.
Furthermore, Lantech, Inc., of Louisville, Kentucky, provides automatic stretch-wrapping devices in its H- and V-Series wrappers which utilize a rotary turntable to displace the palleted materials while the wrapping device remains stationary. These devices, however, utilize an automatic sequencing process which controls the entire wrapping procedure from the entry to the exit of the palletized materials through the wrapping zone.
In practice, the prior art devices are limited in terms of throughput by several factors. One of the many factors affecting the throughput of the device is the necessity to automatically begin and end each wrap cycle without the need for human intervention. Furthermore, the device must smoothly transition from one wrap cycle to the next without human intervention as well. This means the device must move the palletized materials into the wrap zone from a first staging zone, affix the film to the palletized stack, begin the wrap cycle, end the wrap cycle, cut the film, and move the palletized wrapped pallet from the wrap zone into a second staging zone where it can be transferred along down through the distribution channel. Two critical points of this cycle are the affixing of the film to begin the wrap cycle and the cutting of the film to end the wrap cycle. A critical delay in the wrapping process occurs if the film is not in a position for the wrap cycle to begin, which is usually attributable to a failure to leave the film in the proper position at the end of the previous wrap cycle. One embodiment of a prior art device, as exemplified by the Lantech device, utilizes a pincer-type gripper which is typically formed of a set of two pinching jaws located at the low point of the vertical wrapping mechanism travel. This is typically adjacent the level of the pallet as part of the palletized load.
At the beginning of a pallet wrapping cycle, a raw end of film lies adjacent the palletized load which has been recently moved into the wrap zone and in a position for wrapping. This loose or trailing end of film has been severed from the previous stack, by a method to be described later, but has been cut in such a manner so as to allow it to fall within the jaws of the gripping mechanism. As the wrap cycle begins, the gripping mechanism clamps on the film and the film is disposed along the outside of the palletized material. In the example of the Lantech machine, the turntable upon which the pallet is resting begins to revolve while the wrapping mechanism is disposed in a vertical direction to provide a helically wound wrapping layer. This system is, however, just as applicable to mechanisms utilizing a rotary wrapping arm. Once the wrapping procedure is completed and the wrapping mechanism is approaching the home position, the device automatically discontinues the application of prestretch to the film being applied. This allows a section of unstretched film to comprise the terminal portion of the film supply, and provide same as a leading edge to the next cycle. When the swing arm actually comes to the stop position, a cutting armature typically is moved into the wrapping zone adjacent the unstretched film extending between the wrapping mechanism and the palleted material. The cutting armature typically utilizes a heating element of some type to locally melt and sever the film at a particular point. Furthermore, a brush mechanism attached to the cutting armature may be utilized to smooth the recently severed film end along the side of the palleted material. At this time, the free end of the film supply of the wrapping mechanism falls, hopefully into the jaws of the gripping mechanism for the next wrap cycle.
The prior art gripping and cutting mechanism has many limitations and potential areas of failure. More particularly, there are three particular points at which the system may be expected to fail. The first is the failure of the film to fall within the grip of the jaws after the cutting procedure without the ability to grip the film to begin the next wrap cycle. Human intervention is necessary to reset the device at this point and valuable time may be lost. The second potential failure point is the failure of the clamping jaws to retain the film once the wrapping cycle has begun but before the wrap has had an opportunity to establish a grip on the palleted materials. This is typically due to an insufficient grip of the clamping device and more typically because the clamping device has gripped a portion of the film which has been stretched beyond its strength capabilities. The third common potential area of failure is through an insufficient cutting of the film at the termination of the wrap cycle. There are many factors leading to the failure of the film to be completely severed. Most common among these is a contaminated or gummed heating device which is unable to locally melt the film. Typical cutting devices utilize an exposed heated wire or filament for localized melting, which is susceptible to contamination because of its direct contact with the film and the possibility of scrap film adhering thereto. Additional more esoteric problems may include reaction of the film with the heating element or overheating of the cutting element because of film clogging.
What is lacking in the art, therefore, is a device which provides a simple and reliable apparatus and method for efficient gripping and termination of the film load at the beginning and end of each wrap cycle respectively, and one which provides a gripping mechanism which is not dependent upon a fortuitous event such as the landing of the cut film within the jaws; one which allows the gripping device to only grip unstretched film; and finally one which utilizes a cutting device which will reliably perform its cutting operation without risk of contamination in order to provide a consistent, high quality end of the film load.